Modular low cost trackerless spectral sensor

ABSTRACT

A photodiode sensor device and systems. The photodiode sensor device includes a housing portion. The housing portion includes a cylindrical enclosure. A window is disposed at a first end of the housing portion. A filter wheel is within the housing portion. A motor positioned within the housing is adjacent the filter wheel opposite the window. The motor is attached to the filter wheel. A photodiode sensor within the housing portion intermediate the first photodiode sensor and the window. The first photodiode sensor receives filtered light incident on the window and transmit a signal associated with sensed parameters of the filtered light. Also, a hemispherical dome for diffusing the light to a collimating lens has a grating, a focusing lens, and a linear detector array. An exit port transmits light to the collimating lens. The sensor array is opposite the grating for sensing the diffused light.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was developed under Contract No. DE-NA0003525 awarded bythe United States Department of Energy/National Nuclear SecurityAdministration. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

The application generally relates to spectral sensors for solarirradiance. The application relates more specifically to a fixedposition spectral sensor for solar radiation, atmospheric monitoring,sensing of atmospheric particulates and methods of spectral irradianceanalysis for positioning photovoltaic (PV) arrays.

Current photovoltaic (PV) installations require large financialinvestments. To get an improved positive return on the investment, PVtechnology must be better matched to the solar spectral resource at asolar power generating location. Improved matching of the solar spectralresource requires extended monitoring of the solar spectrum using aspectrometer. Solar spectrometers may be expensive and difficult toimplement in practice. Tracking systems that tilt or reposition thespectral sensors require complex mechanical systems and may introduceerror in the data when the positioning systems wear over time.

Site-specific solar spectrum needs to be considered to most effectivelyutilize the solar resources at a given location. Decisions can then bemade on the appropriate solar technology to optimize power generation.The rise of commercially relevant non-silicon thin film PV materialssuch as copper indium gallium selenide (CIGS) and cadmium telluride(CdTe) provides different bandgaps that can be employed for localspectra that can be red- or blue-shifted from the Standard Tables forReference Solar Spectral Irradiances published in ASTM G173 standard.

Furthermore, spectral ratios that differ from the norm can influence theoverall production in multi-junction PV cells by changing the currentlimiting junction. Specific, geographically varying atmosphericcomponents like water vapor and dust aerosols can affect the spectrumand must be accounted for when addressing variations in spectral ratios.After a suitable PV technology is selected for a site, the daily solarspectrum must monitored to accurately predict the performance of the PVsystem Spectrometer systems that are capable of delivering thisinformation are often expensive, require maintenance, delicate, dataintensive, and can be challenging to implement in the field. Variousspectrometers are available on the market.

What is needed is a system and/or method that satisfies one or more ofthese needs or provides other advantageous features. Other features andadvantages will be made apparent from the present specification. Theteachings disclosed extend to those embodiments that fall within thescope of the claims, regardless of whether they accomplish one or moreof the aforementioned needs.

SUMMARY OF THE INVENTION

One embodiment relates to a photodiode sensor device. The photodiodesensor device includes a housing portion. The housing portion includes acylindrical enclosure. A window is disposed at a first end of thehousing portion. A filter wheel is within the housing portion. A motorpositioned within the housing is adjacent the filter wheel opposite thewindow. The motor is attached to the filter wheel for rotating thefilter wheel. A first photodiode sensor is located within the housingportion and positioned intermediate to the first photodiode sensor andthe window. The first photodiode sensor arranged to receive filteredlight incident on the window and transmit a signal associated withsensed parameters of the filtered light.

Another embodiment relates to a non-tracking solar sensor system. Thenon-tracking solar sensor system includes a transparent hemisphericaldome enclosure for receiving light. A diffuser is disposed with theenclosure for diffusing the light. A photodiode sensor array senses atleast one discrete wavelength of the diffused light. A data acquisitionmodule is configured to receive a sensor signal from the sensor array,the signal indicative of light quality at least one discrete wave bandfor processing via a processor module.

Still another embodiment relates to a non-tracking solar sensor system.The non-tracking solar sensor system includes a transparenthemispherical light collection diffuser portion, a collimating lensdisposed adjacent to the diffuser portion, a grating, a focusing lens,and a linear detector array; the diffuser portion having an exit port atone end configured to transmit a portion of light to a collimating lens;the grating disposed between the collimating lens and the focusing lens;the linear photodiode sensor array disposed adjacent to the focusinglens opposite the grating for receiving the diffused light and sensingparameters associated with the diffused light; the photodiode sensorarray configured to transmit the sensed parameters to a data acquisitionmodule.

Another embodiment of a non-tracking solar sensor system would be basedon a convex reflective mirror, an optical collimation lens, and an arrayof optical sensors and filters. In this embodiment, the hemisphericalmirror is placed at the bottom to direct light up into the detectorarray. Optical wavelength separation may be accomplished using dichroicmirrors may be placed to reflect certain portions of the solar spectrumwhile passing others. The ratios of signals between sensors may be usedto describe the overall solar spectrum.

Non-tracking, or stationary, solar spectrum sensors are advantageousbecause most PV plants have the modules on a fixed angle or tilt, andmost do not have access to two-axis trackers because two-axis trackingsystems are generally expensive. This unique fixed position, ortrackerless, design quality also offers potentially ubiquitous adoptionin solar energy applications, as well as in as agriculture, health,weather forecasting and many others. In addition, the disclosed solarspectrum sensors require minimal operating power, and may also beconnected to a tandem, inexpensive solar cell-battery assembly and datalogger.

One more advantage of the disclosure is a novel, inexpensive spectralsensor suitable for outdoor use that accurately monitors the solarspectrum to optimize solar power generation and better predict PVperformance.

Another advantage is the ability to operate the spectral sensor withoutthe need for an expensive solar spectrum tracker to record accuratespectral irradiance measurements from any non-shaded location.Commercial-off-the-shelf items may be utilized.

Another advantage is software developed to process data for optimizingsolar PV and thermal applications. The disclosed spectral sensor alsohas other applications such as ambient background measurement foroptical detection techniques, weather and air quality measurements,visibility data for airports, spectral calibration for satellite imagingsystems, and climate change research for accurate, ubiquitous adoptionand monitoring.

Still another advantage is weather forecasting can also greatly be aidedas it can help address radiative forcing impacts which directly affectthe weather by airborne particulates such as pollution and dust.

Further, the disclosure may improve crop yields due to the impact of thequality of light at certain bands and spectral-light research managementfor enhanced foliage crop productions.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The application will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is an exemplary solar spectral irradiance profile for a solarcell site.

FIG. 2 shows an exemplary embodiment of a non-tracking spectralirradiance sensor including a filter wheel.

FIG. 3 shows an exemplary embodiment of a non-tracking solar sensorusing the sensor of FIG. 2.

FIG. 4 shows an alternate exemplary embodiment of a non-tracking solarsensor with a custom collimating and focusing lens, using the sensors ofFIG. 2.

FIG. 5 shows a comparison graph of the extraterrestrial spectralirradiance a transmittance profile of the measured spectral irradiance.

FIG. 6 shows the reconstructed spectrum from the Spectral TransmissionModel provides a close correspondence with the full-band measuredspectrum.

FIG. 7 shows a comparison of short circuit current between the EKOspectrometer and the measured photodiode data with spectralreconstruction using the Spectral Transmission Model of the presentdisclosure.

FIG. 8 shows an alternate embodiment of a non-tracking solar sensorsystem.

DETAILED DESCRIPTION OF THE INVENTION

Before turning to the figures which illustrate the exemplary embodimentsin detail, it should be understood that the application is not limitedto the details or methodology set forth in the following description orillustrated in the figures. It should also be understood that thephraseology and terminology employed herein is for the purpose ofdescription only and should not be regarded as limiting.

Referring to FIG. 1, a typical solar spectral irradiance forAlbuquerque, N. Mex. is shown. Responsivity of a silicon solar cell, andthe possible discrete solar wavelengths that will be measured with thediscrete spectral sensor are illustrated in FIG. 1. FIG. 1 shows anexemplary solar spectral irradiance 100, and the responsivity curve of aSilicon solar cell. The vertical lines represent the monitored discretebands 102. The discrete spectral bands 102 are typically 10 nm wide,except for the band 102 at 500 nm which is 40 nm wide. A spectrometermeasures the solar spectrum at a high resolution (1-2 nm). Thespectrometer typically uses two different sensors. One sensor measuresshort wavelengths and another sensor measures longer wavelengths, orinfrared radiation (IR). The disclosed system and methods apply aspectral sensor to measure sunlight at several discrete wavelengths,e.g., five or six discrete wavelengths. These discrete wavelengths arepredetermined based on solar spectral analysis. Five discretewavelengths are sufficient for full spectrum reconstruction. The solarspectral bands having the greatest relevance for the spectrometer aredetermined, e.g., based on aerosols, particulates, and precipitablewater in the atmosphere. It should be noted that the disclosedembodiments may be modular and therefore are reconfigurable forselectively sensing solar irradiance in predetermined bands. Byinterchanging the modular photodiodes or filters the solar spectrometercan be tuned as desired to focus on wavelengths or bands of interest forthe particular application.

In an embodiment, five measurements of the solar spectrum are suitableto accurately reconstruct a profile of the solar spectrum. In anexemplary embodiment the discrete wavelengths within the silicon (Si)responsivity curve may be limited. The wavebands may be extended intothe infrared radiation band for other PV technologies or sensorapplications.

The non-tracking spectral sensor eliminates the need for a two-axistracker. A non-tracking sensor may be used in, e.g., PV plant facilitieswithout access to two-axis trackers. With the modular versatility for awide variety of spectral filters that can be utilized for analyzingdiscrete bands across the entire spectrum, as well as the utility of afixed position sensor, a stationary spectral sensor may be implementedfor a variety of locations and applications in many of atmosphericconditions.

Referring to FIG. 2, an embodiment of a non-tracking spectral irradiancesensor 10 including a filter wheel is shown. Spectral irradiance sensor10 may measure up to twelve bands using just one photodiode sensormodule 10. A horizontally aligned filter wheel 12 is disposed within anopaque cylindrical enclosure or housing 11 open at an end 15 and havinga transparent quartz window 13 covering the opening 15, for admittingsolar irradiance. Filter wheel 12 is disposed above a photodiode sensor14, e.g., a spectrum selective Si photodiode sensor. Sensor 14 collectsdata at predetermined intervals, e.g., every twenty seconds. In anembodiment a second sensor 16 may also be utilized, second sensor is notequipped with a filter wheel 12. Second sensor 16 monitors unfiltered,i.e., clear-sky irradiance measurements. If second sensor 16 does notdetect clear-sky conditions, the sensor may transmit a signal to disableprimary sensor 14, beneath filter wheel 12, to prevent it fromoperating, for ensuring the highest quality in data. Filter wheel 12 islinked mechanically to a motor 17 by a shaft 19, for rotating theposition of wheel within enclosure 11.

Referring next to FIG. 3 one embodiment for a non-tracking solar sensoris shown. A dome enclosure 20 is disposed above a diffuser 22 and aphotodiode sensor array 24. The incident solar radiation indicated byarrows 26, 28, 30, is collected within dome enclosure 20. Inside domeenclosure 20 are diffusing elements 22 and baffles 32, which directuniform solar radiation 26, 28, 30, to sensor array 24. Sensor array 24includes multiple solar sensors 10 (FIG. 2) at the bottom of domeenclosure 20. Dome enclosure 20 is substantially transparent andcollects and integrates the incident solar radiation. Sensors transmitanalog signals to a data acquisition module 25. Data acquisition module25 converts the analog signals to digital data and forwards, e.g., viadata link 27, to a computer system, e.g., PC or server, for processingthe digital data.

Referring next to FIG. 4, an alternate embodiment for a non-trackingsolar sensor is shown. Incident solar radiation 26, 28, 30 is collectedwith a custom lens 40. A small exit port 42 at the bottom of the lensdirects a portion of solar radiation light 26-30 to a collimating lens44. Light 26-30 is collected with lens 44 and then transmitted through agrating 46. Grating 46 disperses the light into different spectralorders. A focusing lens 48 is positioned below grating 46 to receive thedispersed light, and focuses the dispersed light on a linear detectorarray 50. Linear detector array 50 includes a plurality of sensors 10(FIG. 2). Analog signals may transmitted and converted to digital datafor processing, as described above with respect to FIG. 3.

Software is used to process the sensor data that is received by sensors10. Sensor data is transmitted first to a data acquisition module 25 forconversion to digital formatted data for processing. Optimizationalgorithms are coupled with atmospheric modeling code and accuratelyreconstruct the solar spectrum. A regression analysis with interactingcoefficients is used to predict, e.g., the PV short-circuit, directlyfrom the sensor measurements. In an embodiment at least four wavelengthbands may be used for correlation to the PV short-circuit current. Themeasurements over these wavebands may be used to verify the form of ashort-circuit current profile.

In an exemplary embodiment a spectrum reconstruction method uses aspectral transmission model based on a condensed version of developedSandia Spectral Transmission Model based on a condensed version ofEquation 1 below:

$\begin{matrix}{I_{{sc},{{Meas}\mspace{14mu}{{Temp}.\;{Corrected}}}} = \frac{I_{{sc},{Meas}}}{1 + {\alpha_{Th}( {T_{cell} - 25} )}}} & {{EQ}.\mspace{14mu} 1}\end{matrix}$

And the measured irradiance E is defined by Equation 2 below:E=r ² T E ₀,  EQ. 2where E₀ is the extraterrestrial irradiance at AM₀ measured above theearth's atmosphere, T is the total atmospheric transmittance affected byattenuation through the atmosphere, and r is the ratio of the average toactual sun to earth distance. In turn the atmospheric transmittance Tcan be estimated from the measured irradiance on the ground by Equation3:

$\begin{matrix}{T = \frac{E}{r^{2}E_{0}}} & {{EQ}.\mspace{14mu} 3}\end{matrix}$

since the extraterrestrial irradiance is fairly constant anywhere abovethe atmosphere.

Atmospheric attenuation may be caused by aerosols, ozone, gases, watervapor, and Rayleigh scattering. Each constituent affects different partsof the spectrum. By using the calibrated values of the photodiodes aswell as the respective values of E₀, according to Equation 3 therespective transmission values are computed as indicated in as presentedin FIG. 5 which shows a comparison graph (a) of the extraterrestrialspectral irradiance compared to the measured spectral irradiance at11:40 am local time on Oct. 1, 2014 in Albuquerque, N. Mex., and thedata from the calibrated spectral sensors, indicated by dots for thesame day and time; and graph (b) shows a transmittance profile of themeasured spectral irradiance shown in graph (a) and the correspondingcalculated transmittance from the photodiode spectral sensors indicatedby dots. Note that the r² factor was not taken into account in thecalculation.

Using this calibrated data of FIG. 5, each of these transmission pointsmay be used to optimize and compute the spectrum according to theirrespective time series values. This functionality of the SpectralTransmission Model computes the spectrum based on fundamentalatmospheric physics. After the optimization algorithm is complete thespectrum may be calculated and compared to the spectral irradiancemeasured by the wide-band EKO spectrometers.

Referring to FIG. 6, based on data taken at solar noon on Oct. 1, 2014,the reconstructed spectrum from the Spectral Transmission Model providesa close correspondence with the full-band measured spectrum. Calculatedspectrum shown on line 60 is based on discrete photodiode measurementsand computation within the Sandia Spectral Transmission Model iscompared with a measured full-band spectrum 65 from an EKO spectrometerfor Oct. 1, 2014. Next, using this data with Eq. 4 one is able tocompare the calculated short circuit current. Referring next to FIG. 7,the results of a comparison of short circuit current between the EKOspectrometer, indicated at line 70, and the measured photodiode datawith spectral reconstruction using the Spectral Transmission Modelindicated at line 75, for Oct. 1, 2014 shows close agreement to within alow RMS error of 0.05.

Referring next to FIG. 8, an alternate embodiment of a non-trackingsolar sensor system 300 is shown. The non-tracking solar sensor system300 includes a convex reflective mirror 302 for receiving incident whitelight 304, and reflecting the light 304 at an optical collimation lens306. Collimating lens 306 directs collimated light rays at an array 314of optical sensors 308 and filters 310. In the embodiment of FIG. 8,hemispherical reflective mirror 302 is shown placed at the bottom ofsystem 300 to direct light 304 upwards into the detector array 314.Optical wavelength separation may be accomplished using dichroic mirrors312. Dichroic mirrors 312 may be placed to selectively reflectpredetermined portions of the solar spectrum while passing others. Theratios of signals between sensors may be used to describe the overallsolar spectrum.

While the exemplary embodiments illustrated in the figures and describedherein are presently preferred, it should be understood that theseembodiments are offered by way of example only. Accordingly, the presentapplication is not limited to a particular embodiment, but extends tovarious modifications that nevertheless fall within the scope of theappended claims. The order or sequence of any processes or method stepsmay be varied or re-sequenced according to alternative embodiments.

The present application contemplates methods, systems and programproducts on any machine-readable media for accomplishing its operations.The embodiments of the present application may be implemented using anexisting computer processors, or by a special purpose computer processorfor an appropriate system, incorporated for this or another purpose orby a hardwired system.

It is important to note that the construction and arrangement of thelow-cost spectral sensor and analyzer, as shown in the various exemplaryembodiments is illustrative only. Although only a few embodiments havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited in the claims.For example, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. Accordingly, all such modificationsare intended to be included within the scope of the present application.The order or sequence of any process or method steps may be varied orre-sequenced according to alternative embodiments. In the claims, anymeans-plus-function clause is intended to cover the structures describedherein as performing the recited function and not only structuralequivalents but also equivalent structures. Other substitutions,modifications, changes and omissions may be made in the design,operating conditions and arrangement of the exemplary embodimentswithout departing from the scope of the present application.

As noted above, embodiments within the scope of the present applicationinclude program products comprising machine-readable media for carryingor having machine-executable instructions or data structures storedthereon. Such machine-readable media can be any available media whichcan be accessed by a general purpose or special purpose computer orother machine with a processor. By way of example, such machine-readablemedia can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium which can be used to carry or store desired program code inthe form of machine-executable instructions or data structures and whichcan be accessed by a general purpose or special purpose computer orother machine with a processor. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or a combination of hardwired or wireless) to amachine, the machine properly views the connection as a machine-readablemedium. Thus, any such connection is properly termed a machine-readablemedium. Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions comprise, forexample, instructions and data which cause a general purpose computer,special purpose computer, or special purpose processing machines toperform a certain function or group of functions.

It should be noted that although the figures herein may show a specificorder of method steps, it is understood that the order of these stepsmay differ from what is depicted. Also two or more steps may beperformed concurrently or with partial concurrence. Such variation willdepend on the software and hardware systems chosen and on designerchoice. It is understood that all such variations are within the scopeof the application. Likewise, software implementations could beaccomplished with standard programming techniques with rule based logicand other logic to accomplish the various connection steps, processingsteps, comparison steps and decision steps.

The invention claimed is:
 1. A photodiode sensor device comprising: ahousing portion comprising a cylindrical enclosure, a window disposed ata first end of the housing portion, a filter wheel disposed within thehousing portion, a motor positioned within the housing adjacent thefilter wheel opposite the window, the motor attached to the filter wheelfor rotating a position of the filter wheel; and a first photodiodesensor disposed within the housing portion, the filter wheel positionedintermediate the first photodiode sensor and the window, the firstphotodiode sensor arranged to receive filtered light incident on thewindow; wherein a second photodiode sensor is disposed on an exterior ofthe housing portion and arranged to sense an unfiltered light fromabove; electrical connections to the sensors for acquiring data signals.2. The device of claim 1, wherein the photodiode sensor is configured tomeasure between one and twelve light frequency bands.
 3. The device ofclaim 1, wherein the filter wheel is horizontally aligned under thewindow.
 4. The device of claim 1, wherein the window comprises atransparent quartz window for admitting light associated with solarirradiance.
 5. The device of claim 1, wherein the photodiode sensorcomprises a spectrum selective Si photodiode sensor.
 6. The device ofclaim 1, wherein the photodiode sensor collects data at predeterminedintervals.
 7. The device of claim 1, wherein the predetermined intervalis every twenty seconds.
 8. The device of claim 1, further comprising asecond photodiode sensor, the second photodiode sensor disposed on anexterior of the housing portion, the second photodiode sensor beingarranged to monitor unfiltered light and transmit light measurementsassociated with solar irradiance.
 9. The device of claim 1, wherein, inresponse to the second photodiode sensor detecting an unclear solarirradiance level, the second photodiode sensor transmits a shut offsignal and the processor disables the first photodiode sensor.
 10. Thedevice of claim 1, wherein, the filter wheel being mechanically linkedto a motor, the motor arranged to rotate a position of the filter wheelto adjust its angle within the housing.
 11. The system of claim 1,wherein further comprising a plurality of baffles, the baffles disposedadjacent a sensor array comprising multiple sensors including the firstdiode sensor and arranged to direct uniform solar radiation to thesensor array.
 12. The system of claim 11, wherein the sensor arraycomprises multiple solar sensors disposed at a bottom end of the domeenclosure, and wherein the dome enclosure is substantially transparentand collects and integrates the incident light associated with solarradiation.
 13. The system of claim 11, wherein the sensor arraytransmits analog signals representing a plurality of parametersassociated with the sensed light to a data acquisition module; whereinthe data acquisition module receives the analog signals from the sensorarray and converts the analog signals to a digital data set and forwardsthe digital data via a data link to a computer system associated withthe processor.
 14. The device of claim 13, further comprising a gratingconfigured to disperse the light into different spectral orders.
 15. Thesystem of claim 14, further comprising a focusing lens positioned belowthe grating to receive the dispersed light, and to focus the dispersedlight on the sensor array; the linear detector array including themultiple sensors in communication with the data acquisition module; thedata acquisition module configured to convert the analog signals to adigital data set for processing by a computer.